1. Field of the Invention
This invention relates to a writing instrument comprising a combination of means for drawing out an eraser and a writing portion.
2. Description of the Prior Art
In a writing instrument such as a conventional knocking type mechanical pencil, in which a rear cap is axially movably connected to a rear end of an outer tube, a lead pipe is axially slidably inserted into the interior formed by both the outer tube and the rear cap, an eraser of which rear end is caulked by a metal annulus is detachably fitted and held on the lead pipe, and the rear cap is knocked through the eraser whereby the lead pipe is axially moved accordingly to feed a lead. The eraser is used by removing an eraser cap from the rear cap.
In such a conventional writing instrument as mentioned above, the whole relatively lengthy rear cap on the extension coaxial with the outer tube has to be knocked when lead is fed. Therefore, there has been a problem in that at the time of knocking, the rear cap is caught by a hand holding the pencil, rendering knocking difficult.
The eraser is always held and fixed in position, and the length thereof projected from the caulked metal annulus is short in view of the strength of the eraser itself. In addition, the amount of drawing the eraser cannot be adjusted according to the degree of consumption, resulting in a problem in that the degree of consumption of the eraser is severe and the eraser soon becomes unsuitable for use.
In view of the foregoing, the present applicant has solved the aforesaid problems by a writing instrument disclosed in Japanese Utility Model Application Laid-Open Publication No. 63-63489 previously filed.
This writing instrument is designed so that when a rear cap connected to a rear end of an outer tube is rotated, an eraser is fed out by the screw feed action, and a knocking cap inserted axially slidably into the rear cap and extended outwardly of the rear end is knocked to thereby feed a lead.
However, the above-described writing instrument has a problem in that when the eraser is fed by rotation of the rear cap after the knocking cap has been knocked, the knocking cap is also moved therewith. Therefore, an engaging rib is provided. However, in the case where the friction between the eraser and the knocking cap is greater than the engaging rib, there remains a problem in that the knocking cap is moved, resulting in a lowering of reliability during mass production.